Meta Title: Best Tankless Reverse Osmosis Systems of 2024 | Water Defense
Meta Description: Read our in-depth reviews of the best tankless RO systems on the market. We cover contaminant removal rates and everything else you need to know!
Tankless reverse osmosis (RO) systems are a great way to enjoy the benefits of RO-filtered water without using up too much space in your home. Plus, as they don’t require a tank, they tend to be easy to install and require very little maintenance.
We’ve spent a lot of time testing all the best tankless RO systems out there and we’ve put together this list to show you the results.
The winner is the AquaTRU Countertop RO System because of its 4-stage filtration system that effectively removes up to 99% of contaminants. We also love that it requires no installation and that it’s the most affordable tankless RO unit we’ve come across.
But, if you live in a home with particularly high water demands, then you'll appreciate the incredible 800GPD flow rate of the Waterdrop G3P800. Or, if you want a tankless RO system that produces instant hot water, you'll find what you're looking for with either the RKIN U-1 or the Waterdrop K6.
- Filtration process: 4-stage
- Filtration capacity: Not specified
- Wastewater ratio: Also not specified
- NSF certifications: The manufacturer states that it’s NSF-certified but doesn’t list which ones
- Size: L: 38.9”, W: 26.9”, H: 41.9”
- Warranty: 1 year
- Filtration process: 5-stage
- Filtration capacity: 200 GPD
- Wastewater ratio: 1:1
- NSF certifications: None
- Size: L: 19”, W: 9.5”, H: 17”
- Warranty: 1-year
- Filtration process: 7-stage
- Filtration capacity: 800 GPD
- Wastewater ratio: 3:1
- NSF certifications: NSF/ANSI Standards 42, 53, 58, and 372
- Size: L: 18.06”, W: 5.65”, H:17.75”
- Warranty: 1-year warranty with a 30-day return guarantee
- Filtration process: 5-stage
- Filtration capacity: 600 GPD
- Wastewater ratio: 2:1
- NSF certifications: NSF/ANSI Standards 372
- Size: L: 18”, W: 7”, H:17”
- Warranty: 1-year warranty with a 30-day return guarantee
Tankless Reverse Osmosis Systems
AquaTRU Countertop RO System
- Filtration process: 4-stage
- Filtration capacity: Not specified
- Wastewater ratio: Also not specified
- NSF certifications: The manufacturer states that it’s NSF-certified but doesn’t list which ones
- Size: L: 38.9”, W: 26.9”, H: 41.9”
- Warranty: 1-year
PROS
- It uses 4-stage “Ultra Reverse Osmosis” tech to remove lots of contaminants including arsenic, lead, fluoride, and PFAS
- The filters have good longevity and can last between 6 months to 2 years before they need to be replaced
- It includes indicator lights that tell you when you need to replace the filters
- It doesn’t require any installation or plumbing which saved us time and money
- It’s sleek and compact, meaning it can fit on most kitchen countertops
- The plastic components are BPA-free, so there’s no risk of BPA leakage into your water
CONS
- We’ve seen several reviews from customers who say they had leaking issues with their units. However, we didn’t experience this during our tests.
The AquaTRU Countertop RO System tops our list for several reasons. First of all, its 4-stage filtration process is able to remove up to 99% of contaminants commonly found in US water supplies such as lead, arsenic, and chlorine. This eradicates the issues associated with these contaminants like staining and bad tastes and odors. That’s not all, though.
We also like that it requires no installation and is incredibly easy to maintain. So, if you’re looking for a highly efficient RO system that requires minimal fuss, we think you’ll love this unit.
Advanced Filtration
Of course, the first thing we evaluate when testing filter systems is how effective the filtration process is. We have to say that we were impressed by this unit’s 4-stage “Ultra Reverse Osmosis” tech, which enables it to remove up to 99% of contaminants. Let’s take a look at how it works:
- Firstly, the water passes through a particulate pre-filter that removes organisms and sediment
- Then, it passes through an activated carbon pre-filter to remove any chlorine and chemical disinfectants
- Next, the water comes into contact with the reverse osmosis filter that gets rid of contaminants like arsenic, lead, and chromium 6
- Finally, the water reaches the activated carbon VOC filter that removes contaminants like pesticides and PFAS.
The water we sampled from this system was clear and clean, and we didn’t detect any odors that are usually present in contaminated water.
No Installation and Very Low Maintenance
One of the best things about the AquaTRU Countertop RO System is that you don’t have to install it or mess around with any plumbing. Although most filter systems are fairly easy to install, you often need to call a plumber to do it properly. With this system, there’s no need to pay a plumber to get it up and running.
Plus, as it’s an RO system, it doesn’t need to be topped up with salt or chemicals. The filters also last for around 6 months in homes with high water demand, so there’s barely any maintenance required once you’ve set it up.
LED Indicators
The LED indicator lights make it easy to tell when the filters need to be replaced. This is very helpful—worn-out filters lead to lower water quality, as they can no longer achieve the same contaminant removal rates as new filters. With this system, we knew exactly when it was time to replace them so the water quality never decreased.
RKIN U-1
- Filtration process: 5-stage
- Filtration capacity: 200 GPD
- Wastewater ratio: 1:1
- NSF certifications: None
- Size: L: 19”, W: 9.5”, H: 17”
- Warranty: 1-year
PROS
- Like the AquaTRU model, it can remove up to 99% of contaminants including heavy metals, chlorine, and fluoride
- It has an intelligent touch control pad that makes it easy to monitor the water quality and the health of the filters
- It’s highly versatile and can provide instant hot water, cold water, and negative ORP water
- As with the AquaTRU unit, there’s no installation required and very little maintenance
- Its filtration process includes UV, hydrogen tech, and RO, which is highly advanced when compared to other more basic models
CONS
- It wastes 0.5 gallons of water for every 0.5 gallons of pure water it produces which means it’s not an eco-friendly option
- It doesn’t have any NSF certifications, which means it hasn’t been independently tested
The RKIN U-1 is a very advanced unit that combines RO filtration with UV and hydrogen tech and, like the AquaTRU unit, can remove up to 99% of contaminants. The main reason it’s second on our list is that it’s pretty wasteful. If you want an eco-friendly RO system then this probably isn’t the best choice.
Yet, if you like the sound of a versatile RO system that provides hot and cold filtered water, you’ll be impressed with this unit.
RO, UV, and Hydrogen Technology
The most outstanding thing about the U-1 is that it doesn’t just rely on RO filtration to provide clean and healthy water. It also utilizes a sediment filter, an activated carbon filter, and an alkaline post-filter. At the end of the filtration process, there’s an optional hydrogen infusion stage that you can turn on and off.
When we turned it on during testing, we ended up with hydrogen-enriched water that tasted clean and crisp. We also like that there’s a UV light to keep the water fresh whenever the system isn’t being used. This is a great touch as filtered water can start developing bacteria when left standing.
Intelligent Control Panel
When it comes to its digital interface, the U-1 definitely outperforms the AquaTRU unit. Instead of LED indicators, it has a digital control panel that you can use to adjust numerous settings including water temperature. You can also use it to monitor the quality of your water, keep track of your home’s water consumption, and find out when your filters need to be replaced.
To be honest, this is such a helpful feature that we wish every water filter system included. Unfortunately, we rarely come across systems with digital interfaces as good as this during our tests. So, we were super happy that the U-1 included this feature and it’s one of the main reasons it earned second place on our list.
Waterdrop G3P800
- Filtration process: 7-stage
- Filtration capacity: 800 GPD
- Wastewater ratio: 3:1
- NSF certifications: NSF/ANSI Standards 42, 53, 58, and 372
- Size: L: 18.06”, W: 5.65”, H:17.75”
- Warranty: 1-year warranty with a 30-day return guarantee
PROS
- Extremely effective seven-stage filtration process including a UV sterilizer that kills 99.9% of bacteria and viruses
- Compact design and really easy to install
- NSF-certified, which means its contaminant removal capabilities have been independently tested
- 800 GPD filtration capacity, so it’s suitable for larger homes with high water demands
- 3:1 wastewater ratio, which makes it a much more eco-friendly option than the U-1
CONS
- Only one year of warranty, which isn’t particularly reassuring
- Removes healthy minerals but this is a common downside of RO systems
- It’s a lot more expensive than the AquaTRU unit even though it’s a slightly less efficient model
This super compact unit produces 800 gallons of clean water daily and efficiently removes the most prominent tap water contaminants thanks to its seven-stage process. We particularly like that it includes a UV sterilizer for eliminating viruses and bacteria. It’s a great option if you have a fairly high budget and a household with around 4 people.
Key Features:
- 7-stage filtration: The system passes water through a polypropylene cotton layer that blocks sediment and large particles before it reaches a scale inhibitor layer that diminishes hard water molecules. Then, it passes through an activated carbon block that takes care of aesthetic impurities like color and chlorine. Next, the water comes into contact with a second polypropylene cotton layer that removes any remaining sediment particles, and then a 0.0001-micron semipermeable reverse osmosis membrane that eviscerates hazardous chemical contaminants and heavy metals. Finally, the water reaches a post-activated carbon block that handles turbidity and the UV sterilizer that eliminates pathogenic organisms like bacteria and viruses.
- NSF-certified: The Waterdrop unit has NSF certifications (NSF/ANSI Standards 42, 53, 58, and 372) supporting its scientific claims. Plus, it has a detailed performance data sheet listing the contaminants it removes with their reduction rates.
- Excellent flow rate: We also like this WaterDrop product because it doesn’t compromise water flow when dealing with contaminants. It produces a single cup of water in under six seconds, and its filtration capacity of 800 gallons per day (GPD) is unprecedented in the niche.
- Eco-friendliness: RO systems usually waste lots of water during filtration, but WaterDrop G3 P800’s 3:1 wastewater ratio (wasting one cup of water for every three cups of clean water) is among the lowest on the market.
Waterdrop k6
- Filtration process: 5-stage
- Filtration capacity: 600 GPD
- Wastewater ratio: 2:1
- NSF certifications: NSF/ANSI Standards 372
- Size: L: 18”, W: 7”, H:17”
- Warranty: 1-year warranty with a 30-day return guarantee
PROS
- Like the U-1, it can provide both cold and hot water (which is perfect for making coffee)
- Its 600 GPD flow rate means it’s suitable for both small and large homes
- Includes a faucet with a smart display that gives you information about TDS levels and the condition of the filters
- It has built-in limescale prevention, so it requires very little maintenance
- Its 5-in-1 filter is great at removing contaminants like heavy metals, fluoride, and TDS
CONS
- It has a 1-year warranty rather than a lifetime one, which means you have to pay out for repairs if anything goes wrong outside this period
The Waterdrop K6 is the final tankless RO system on our list but that doesn’t mean it’s not a really good device. We like that it’s as versatile as the U-1 and that it includes a smart display faucet.
We’d recommend the K6 if you’re looking for an under-sink tankless RO system that’s slightly more affordable than the G3P800, and that supplies hot water on demand.
Key Features:
- Smart display faucet: While the digital display isn’t quite as good as the U-1’s, it’s still much better than the AquaTRU unit’s indicator lights. With just a few finger taps, we were able to adjust the temperature and monitor important information like the levels of TDS in the water supply.
- 600 GPD flow rate: Again, this doesn’t quite match up to the U-1 but a 600 GPD flow rate is still really high for a tankless RO system. This means there’s no need to wait around for water, and the unit can easily deal with large households.
- 5-in-1 filtration: The K6’s filtration process includes a PP cotton pre-filter, a granular activated carbon filter, and an RO membrane. This allows it to filter out contaminants such as sand, rust, chlorine, heavy metals, and PFAS really effectively
- Instant hot water: We enjoyed using the K6 to make soups, and it’s ideal for teas and coffee. Rather than waiting around for water to boil, you can fill your cups and pans with hot water instantly. We were also impressed with the fact that the water temperature ranged from 104℉-203℉, which we could control with the smart display faucet.
Frequently Asked Questions
Let’s answer the most frequently asked questions regarding tankless reverse osmosis systems.
In the RO process, the devices push the incoming water through a semipermeable membrane. Although the pore size of this membrane changes depending on the manufacturer and model, it’s often 0.0001 microns.
With such a microscopic pore size, contaminants with larger molecules can’t make their way through. So, RO membranes only allow water particles to pass to the other side.
Most reverse osmosis systems utilize a 0.0001-micron pore size. That microscopic pore size blocks many contaminants, from the smallest total dissolved solids to the large particles of rust or heavy metals like lead.
Yes, reverse osmosis removes healthy minerals from water. That’s why some manufacturers include a remineralizer or an alkalizer in their filtration processes.
Healthy minerals such as calcium, magnesium, and bicarbonates are essential for our health and necessary in our diets. Plus, they make the water alkaline. When removed, the water becomes acidic, one of the main criticisms against the RO process.
RO systems with tanks provide contaminant-free water on demand without any dip in water flow since there’s always some clean water on standby. In contrast, tankless units take more time to fill a single cup.
Even tankless systems with the highest filtration capacity, like WaterDrop G3 P800, will take at least six seconds to fill a cup with water. On the other hand, systems that come with tanks will do it in one or two seconds.
However, systems that feature tanks take up too much space. A bulky unit like that is also not suitable if you want something to take with you when you travel. Tankless systems, on the other hand, are compact and portable.
If you’re worried about contaminants in your water and are short on space under your sink, you should buy a tankless RO unit.
On average, you can purchase a tankless RO unit for about $500. However, the price range of the devices on our list is $381.95 to $759.
Our favorite product, the AquaTRU Countertop RO System, costs $381.65, which means it’s the best and most affordable unit on our list.
Conclusion
Tankless RO systems are an excellent way to access contaminant-free water without sacrificing too much under-the-sink space. That’s why they have been so popular lately.
When it comes to choosing one for your home, we couldn’t recommend the AquaTRU Countertop RO System more highly. Its 4-stage filtration tech is really effective at removing contaminants and it doesn’t require any installation. Plus, despite being the best unit we tested, it’s also the cheapest!
On the other hand, The WaterDrop G3 P800 Tankless RO System is the best device in its category for flow rate and eco-friendliness. It has a huge 800 GPD filtration capacity and a 3:1 wastewater ratio. However, at $759, it’s way more expensive than the AquaTRU unit.
